SV-POW! … All sauropod vertebrae, except when we're talking about Open Access

The new Argentine titanosaur was about the same size as the biggest Argentinosaurus

May 19, 2014

You’ve probably seen a lot of yapping in the news about a new “world’s largest dinosaur”, with the standard photos of people lying down next to unfeasibly large bones. Here’s my favorite–various versions of it have been making the rounds, but I grabbed this one from Nima’s post on his blog, The Paleo King.

The first point I need to make here is that photos like these are attention-grabbing but they don’t really tell you much. Partly because they’re hard to interpret, and partly because they almost always look more impressive than they really are. For example, I am 6’2″ tall (1.88 meters). If I lie down next to a bone that is 7’2″ (219 cm) 6’8″ (203 cm) long, it is going to look ungodly huge–a full half a foot longer than I am tall. But that is the length of the femur of the Brachiosaurus holotype–we’ve known of sauropod femora that big for a century now. People get tripped up by this sort of thing all the time–even scientists. Update: even me! Somehow I had gotten it into my head that the Brachiosaurus femur was 219 cm, when it is actually 203 cm. That goof doesn’t affect any of what follows, because from here on down I used Argentinosaurus as the point of reference.

Second point: at least some of the reporting on this new find has been unusually–and refreshingly–nuanced. The first news story I read about it was this one, which gives Paul Barrett plenty of airtime to explain why we should be cautious about jumping to any conclusions regarding the size of the new animal. That will turn out to be prophetic.

But let’s get back to that photo. Just eyeballing it, it looks like the femur is about half again as long as the dude is tall (the dude, BTW, is Pablo Puerta, for whom Puertasaurus is named). I was reading Nima’s post and he guessed that the femur was in the neighborhood of 3 meters, which would be a significant size increase over the next-biggest sauropod known from fossils that still exist (i.e., not including semi-apocraphyal gigapods like Amphicoelias fragillimus and Bruhathkayosaurus). The current based-on-existing-fossils record-holder is Argentinosaurus–there is a partial femur that would have been about 2.5 meters long when complete. So a 3-meter femur would be a wonderful thing. But alas, it just ain’t so–or at least the one in the photo isn’t anywhere near that big. Allow me to demonstrate.

Here’s another copy of the photo with some measurements applied. There is no actual scale bar in the picture, but we can use the dimensions of the things we can see to figure some stuff out.

For starters, there is a lot of perspective distortion going on here. Pallet B is 350 pixels wide at the near end, 280 pixels at the far end–a difference of 20%. I didn’t put the far-end measurement for Pallet A into the picture, but from corner to corner it is 295 pixels.

Shipping pallets vary in size around the world, but in the US the most common size is 48 x 40 inches. Other countries use different sizes, mostly smaller; I am unaware of any standard shipping pallets larger than 48×40. So assuming that the ones in the picture are that size is actually a liberal assumption that will lead to large estimates–if the pallets are smaller than 48×40, then all of the dimensions I’m about to calculate will be smaller as well. Obviously the pallets have their narrow ends facing us, which is nice because 40 inches is almost exactly 1 meter. So we can divide other things in the picture by pallet length and get their dimensions in meters.

The near side of the femur is pretty much in line with the stringer running left-to-right down the middle of Pallet A. From the measurements of the ends of that pallet, we’d expect the middle-distance width to be about 330 pixels, and in fact I got 335. The 830-pixel line I drew on the near side is not the total length of the bone–you could add a bit more for the femoral head, to a max of maybe 860 or 870 pixels. Divide that by 335 and you get a max length of about 2.6 meters.

The 800-pixel line for the far side of the femur goes from the top of the head to the bottom of the medial condyle, so there’s no extending needed there. That line is at about the mid-point of Pallet B, or about 315 pixels. If Pallet B is a meter wide, the femur is 2.5 meters long.

We can also check things by trying to figure out how tall Pablo Puerta is. At first that looks more encouraging for the possibility that this is a record-breaker. If we assume the femur really is 3 meters long, and compare the 800-pixel femur line to the 500-pixel Pablo line, Pablo is 62.5% the length of the femur, or 1.87 meters–about the same height as me. That would be pretty tall for an Argentinian, but it’s certainly plausible.

But that’s not a legit comparison, because Pablo is farther from the camera than is the femur. Look at Pallet A–we can use the slats as perspective guides to help figure out where the proximal end of the femur ought to be if projected back to Pablo’s distance from the camera. If we do that at both ends, the length of the femur if placed where Pablo is lying would be 750 pixels or fewer, which would make Pablo at least 2 meters tall. People get a lot taller than that, but it would make him unusually tall, and if you’re trying to emphasize how big your sauropod is, you probably won’t pick the tallest person in the room to pull a Jensen. If we assume Pablo’s about 5’8″–average height for an Argentinian male–then the femur is about 2.6 meters long, which is consistent with the estimates from the pallets. He could well be shorter, in which the case the femur might also be shorter.

There are of course vast amounts of uncertainty in all of this. I have heard the number 2.4 meters thrown around in the media, which is within the margin of error of my crude estimates here–I deliberately skewed large at most decision points to give the hypothesized 3-meter femur the best possible chance. I have to emphasize that this is not how you do science–I’m deliberately doing this quick and dirty. But even using these admittedly flawed and somewhat goofy methods, it’s easy to show that the femur isn’t 3 meters long, or anywhere near it.

So, three last points:

As the post title implies, the new Argentine titanosaur is about the same size as Argentinosaurus. That shouldn’t be too surprising, since the mass estimates that have been quoted in the media are within a few percent of the mass estimates for Argentinosaurus. The new critter might be a hair bigger, but it doesn’t “smash” the record, and when we get actual measurements it could end up being smaller than Argentinosaurus in linear dimensions. I note that the size trumpeted in the media is a mass estimate based on femoral fatness, not femoral length. You’d think that if the biggest femur was demonstrably longer than the 2.5-meter Argentinosaurus femur, they’d lead with that. So the reporting so far is also consistent with an animal about the same size as Argentinosaurus.

That is in no way a disappointing result! That biggest Argentinosaurus femur is incomplete, so the 2.5-meter length is an estimate. Even if the big femur shown here is only (only!) 2.4 meters long, it’s still the longest complete limb bone from anything, ever. And even if the new animal is identical to Argentinosaurus in size, there’s still a lot more of it, so we’ll get a better idea of what these super-gigantic titanosaurs looked like. That’s a big win.

Finally, this is not a case of MYDD. There’s no paper yet, and I don’t blame the team for not making the measurements public until the work is done. I also don’t blame them for publicizing the find. So far, this seems to be exactly what they’re saying it is–an animal about the size of Argentinosaurus, and maybe just a hair bigger. That’s cool. I wish them the best of luck writing it up. I almost wrote “I can’t wait to see the paper” but actually I can–something like this, I’d rather they take their time and do it right. It may not be a record-smasher, but it’s a solid, incremental advance, and science needs those, too.

But since the bone is closer to the camera than the human, that’s an overestimate. Let’s take off maybe 10% for that — it seems reasonable that Puerta’s distance behind the femur is on the order of 1/10 the distance from the camera — which gives us a raio of 1.51.

Finally: while I agree with Matt there’s point in getting snitty about the lack of actual measurements in a press release (as opposed to an actual paper) — still, wouldn’t it have been cool of them to say “The longest femur is 2.57 m long” or whatever? I’m not sure what would be the reason for not doing this.

“he controversy surrounds slide 6 of this presentation, with the BICEP foreground analysis evidently relying on scraping data from this slide.”

“He built his foreground models as did the BICEP2 team by scraping data out of Keynote™ presentations posted on the web! I have to say that again: The Planck team showed some maps of foregrounds in some Keynote presentations and posted them on the web. Flauger (and also the BICEP2 team before him) grabbed those presentations, scraped them for the all-sky maps, calibrated them using the scale bars, and worked from there.”

“this work appears to definitely involve new heights in the technology of data-scraping from Keynote presentations.”

“Seems to me we’re now stuck with Planck saying they think this is dust, BICEP saying they think it’s not. Planck is the side that has data about dust, BICEP is the side that has something they scraped off a slide of a Keynote presentation…”

you get the idea (see the post at the link for attributions of these quotes). If only the data were available…

This a cool find, indeed. For what I could see in the online photographs, it is not just the femur that has been uncovered. There’s lot more of the animal preserved.
I was wondering, what kind of track would this animal leave? I mean the length and width of the foot? I did find pretty big Albian sauropod (probably titanosaur) footprints in Pula (some 135-145 cm long).

Meanwhile, this short video from The Guardian has a caption that explicitly mentions “the 2.4-metre-long femur bone”.

BTW., Janensch (1961:207), in Table 12, gives the lengths of nine Giraffatitan femora as between 37.5 cm (for Ng 21) to 214 cm (for XV 1). This largest exceeds the lengths of the femora in the SII mount, which Janensch (1950b) gives as 189 cm (on the left, from locality Ni; Janensch thought this was a bit too short for the skeleton) and SII’s own partial right femur, restored to a full length of 196 cm.

So a 2.4 m bone would be 22% longer than that of SII and 12% longer than that of XV 1. If the new beast was build along the same lines as Giraffatitan, that would equate to mass 84% greater than that of SII and 30% greater than that of XV1. Based on my own (2009) estimate of 23337 kg for SII, that would give an estimated mass of 42846 kg, or about 43 tonnes, for the new critter. But titanosaurs tend to be proportionally bulkier than brachiosaurs, so that figure is likely too low.

wouldn’t it have been cool of them to say “The longest femur is 2.57 m long” or whatever? I’m not sure what would be the reason for not doing this.

I strongly suspect that they didn’t do this because the longest femur is actually 2.4 meters long, and therefore shorter than the big Argentinosaurus femur, but maybe fatter. Otherwise I cannot fathom why you’d lead with something as ethereal as a mass estimate derived from a femoral circumference. I would think that if you really had the world’s longest sauropod limb bone, you’d just come out and say that.

BTW., Janensch (1961:207), in Table 12, gives the lengths of nine Giraffatitan femora as between 37.5 cm (for Ng 21) to 214 cm (for XV 1)….and SII’s own partial right femur, restored to a full length of 196 cm.

Wacky. Somehow I had it in my mind that SII femora were the same size as the B. altithorax femur, which is 219 cm. For me, the moral of that comparison is that we don’t give B. a. enough credit these days; it is still an astoundingly big animal.Update: as Mike points out in the next comment, I had my wires crossed on the size of the B. altithorax femur; the largest Giraffatitan femora are longer, not shorter.

As someone who is very definitely under the average height for most males almost everywhere, but otherwise fairly normally proportioned, I hereby offer my services for future Jensen shots of normal-sized sauropods that want to feel better about themselves.

Well, this is embarrassing. Somehow I had gotten it into my head that the B.a. femur was 2.19 m. But now I can’t find a single source, anywhere, to support that. Every published source I can find from Riggs onward–including my own dissertation!–says 2.03 m.

What’s worse is that I also used the 2.19 m measurement in my “reveal” post on the Recapture Creek femur, which I estimated at 2.2 meters. So if the B.a. femur is 2.03 m, then the Recapture Creek femur was ~8% bigger. So maybe Jensen called that right after all.

Jeez, after all of the post-fixing I have to do, I may just go live in the Himalayas for a while. What a maroon.

Agreed! And as long as we’re on that, I heard from Ken Carpenter that Pablo Puerta is in the neighborhood of 5’4″-5’6″ (163-168 cm). So the 2.6-meter estimate is really pushing the edge of what’s possible, and the 3-meter estimate is off the table for good. I suspect that the 2.4-meter measurement from the media will turn out to be accurate–it’s a good fit for the photo, and it would explain why the team didn’t lead with the femur length in the press release.

If your point is that someone needs to take a tape measure to this thing, I fully agree. Right now there’s not much we can do besides wait for the paper.

I know it’s tempting to guess or second-guess the size, but you don’t mention the most amazing thing, which is (according to the BBC write-up) that they seem to have discovered about 150 bones belonging to several individuals, ‘in remarkable condition’. Given the lamentably fragmentary remains of most titanosaurs, surely this is by itself an extraordinary opportunity to better understand the very biggest of the supergiant sauropods.

I did mention it: “And even if the new animal is identical to Argentinosaurus in size, there’s still a lot more of it, so we’ll get a better idea of what these super-gigantic titanosaurs looked like. That’s a big win.”

Diego Pol is explaining that you need femoral and humeral diameters to estimate mass. I think they might be using the methods of Campione and Evans (2012), recently used in Benson et al (2014) and itself based on Anderson et al. (1985). That requires ‘total circumference of the stylopodia (humerus + femur)’ and uses ‘minimum circumference (thinnest region along the diaphysis) as a proxy for limb robusticity’ (both quotes from Campione and Evans (2012)).

The equation used is:

logBM = 2.754⋅logC(H+F)−1.097

Campione and Evans (2012) get a result of 35780kg for ‘Brachiosaurus brancai’ HMN SII using this equation with humerus minimum circumference H 654mm and femur minimum circumference F 730mm.

Diego and colleague in the video say that the longest humerus found has a minimum circumference of 79cms, so 790mm and about a 21% increase on SII.

Benson et al 2014 also have (in a pretty comprehensive limb measurement/mass estimate dataset) a femur minimum circumference F of 940mm for Brachiosaurus altithorax FMNH P 25107, with a length of 2030mm. This is nearly 29% bigger than for Giraffatitan brancai HMN SII (same F=730mm as before, no femur length given). No humerus circumference measurement H for Brachiosaurus though, but the humerus length is 2040mm, shorter than the 2130 for HMN SII. (Does this indicate different proportions between Brachiosaurus and Giraffatitan, or that the specimens examined are composites with wrong hindlimb/forelimb proportions? Or is it just noise?). They give 56000kg for Brachiosaurus altithorax FMNH P 25107 (with estimated H) and 34000kg for Giraffatitan.

Benson et al 2014 also use F=1114mm for Argentinosaurus huinculensis, along with a femur length of 2250mm. No H or humerus length though. There is also no mass estimate for Argentinosaurus so I guess Pol and colleagues must have estimated the missing H, in the manner Benson and colleagues did to get H for Brachiosaurus, to come up with the 70000kg Argentinosaurus estimate that the new beastie just beats.

From this data, it should be possible to solve the above equation to find the femur circumference F, using 77000kg as the mass as stated in the video and elsewhere. If you really wanted the limb lengths, you could then further use the results presented in Campione and Evans (2012) on interspecific limb scaling to infer lengths of these bones; as far as I can see only masses were inferred for the dinosaur taxa they looked like but the plots and regressions of the mammals and reptiles could be used for this.

A final note – quite a few of the direct quotes from the team seem to be discussing the largest dinosaur or the heaviest dinosaur, not the tallest dinosaur or the dinosaur with the longest limb bones, so I’m fairly certain that’s why they aren’t discussing the limb bone lengths. I guess this means that they are confident they have the former but not the latter. Either way I can’t wait for the paper!

We don’t really know how tall Pablo Puerta is, or whether he is “average” or not. That’s the first big problem.

The second is that we don’t know how many of these femurs exactly they found at the site, and if there are more still awaiting recovery there. And which one exactly is the 2.4m one.

Third, since the Argentinosaurus femur is incomplete, there will still be some margin of error depending on which titanosaurs you use as reference. It will be long if you go based on Traukutitan, Alamosaurus, or the big referred Argyrosaurus femurs at the Field Museum. It will be short if you use stocky ones like Saltasaurus or Ampelosaurus as a basis. How basal or derived Argentinosaurus is, still looks pretty debatable to me.

Fourth, even if the big pallet femur is only 2.4m (I doubt it for now) then this animal still may be heavier than Argentinosaurus since the femur is more robust and from the shape and position of the lateral bulge, it also looks like a lognkosaur femur… so basically a walking whale. We really need to see some vertebrae to make a solid assessment of its family though.

There is indeed a lot more of this animal, it’s the most complete thing this big (there’s some hip and even shoulder material visible in the dig site photos) so from that point of view it’s a huge step forward in understanding titanosaurs of this size, no matter how it stacks up next to Argentinosaurus, Puertasaurus, Alamosaurus, etc.

Thanks, Ian, for this very comprehensive comment. I admit to my shame that I’ve never read Campione and Evans (2012) or Benson et al. (2014), though Anderson et al. (1985) is an old favourite.

I’m amazed that the two more recent papers have got such high estimates for brachiosaurs, which have the most gracile humeri of all sauropods. Back in the day, Russell et al. (1980:171) used broadly similar methods to get a truly emaciated estimate of 14.9 tons for Giraffatitan, so something funny is going on somewhere!

[…] of dinosaur is all over the news. These two blog posts will give you some good perspective. First: The new dino isn’t much bigger than the previous “biggest dinosaur”. Second, the coolest part isn’t the size of […]

Mike – Anderson et al 1985 give 29336 kg for HMN SII, so not too different to the recent papers.

CoherentSheath – thanks, I gave up trying to solve on my phone! That’s less than the Argentinosaurus F femoral circumference in the Benson et al 2014 data so not sure how or why this comes out as heavier – is there a very slim Argentinosaurus humerus out there? Or does the new critter have enormous femur proportions?

(Ignore last sentence of my last comment, as CoherentSheath just calculated that it had a slimmer femur than Argentinosaurus so the slim Argentinosaurus humerus is the only option, does this exist? … Unless Pol et al are calculating 70 tons for some other species – is it only us assuming their 70 ton previous heaviest dinosaur is Argentinosaurus?)

It’s well worth reading – I just came across it tonight looking for humeral circumference data for sauropods with which to compare the sole actual datapoint from the new Argentitanopod – and contains the chilling warning for femur-length estimators around the world: “Among commonly cited proxies of size is femur length (…). However, our analyses indicate that length measurements are generally poor indicators of size, especially compared to circumference. Femur length exhibits an especially high amount of error, with a 70% mean PPE [percent prediction error] in living mammals and reptiles, compared to the 25% for the combined humeral and femoral circumference. Caution should therefore be taken when using limb length as size proxies, especially when examining taxa that encompass a wide phylogenetic bracket”.

That’s less than the Argentinosaurus F femoral circumference in the Benson et al 2014 data so not sure how or why this comes out as heavier – is there a very slim Argentinosaurus humerus out there?

As far as I know, there is NO Argentinosaurus humerus out there. Which is obviously a problem if the method requires both humerus and femur circumferences.

Nima:

Fourth, even if the big pallet femur is only 2.4m (I doubt it for now)

Why? Did I screw up in my analysis, or do you know (or just hope) something that I don’t?

If anything, the 2.4-meter length for the pallet femur seems more and more plausible as time goes on. I heard from another friend that Pablo Puerta is just over 5 feet tall, not 5’6″ and certainly not 5’8″. Now, this just more hearsay, and I suppose the femur could still be in the realm of 2.6 meters. But it can’t be much bigger than that without implying both a significantly taller Pablo Puerta than any eyewitnesses can confirm, and significantly non-standard cargo pallets.

Everyone:

Here’s something: in none of the field photos with people lying next to femora do any of the bones overtop the person by as much as the one in the pallet photo. But those field photos also have other people lying down next to the bones, like Diego Pol, who is about average height. So either the _only_ photo of the monster femur is the one on the pallets, or it was also photographed in the field next to someone taller than Pablo Puerta, where it just looked less impressive.

Sauropods are well beyond the end of the range of data on which limb bone allometry equations are based. There are error bars associated with any mass estimation technique, even if the people reporting the numbers don’t pass them along. And the error bars get bigger rapidly as you go beyond the end of the data. For these big titanosaurs, we’re almost an order of magnitude outside the data on which the equations were built. Anyone who thinks there is a meaningful difference between a 70-tonne and a 77-tonne estimate is statistically illiterate–at that remove from any actual data, both of those estimates are within the range of possbility for a single individual.

Argentinosaurus could plausibly be anywhere from 60 to 90 tonnes–we’re talking about an animal known from about eight vertebrae, a fibula, a femur, and not much else. There is a LOT of blank canvas there that we can’t address with our current knowledge. And the new animal is better represented–150 or so bones from multiple individuals–but even less well-known, since all we have to go on so far are the mass estimate and some photos. I mean, we’re all trying to reverse-engineer these things to figure out basic stuff like how long the bones are. And what we’re learning is that with the level of precision that we can muster at this early stage, it seems to be about the same size as Argentinosaurus. There is so far NO evidence that it was significantly bigger.

Matt – the Campione and Evans paper compares mass estimates of tetrapods using various combinations of femur and humerus length and circumference, across a huge range of extant and extinct tetrapods, and tests the predictive power of various body mass estimation equations. You don’t need both humerus and femur but a combination gives best results – the best mass predictor is Femur * Humerus circumference (r2 of 0.988 on log-log regressions… and predicted % error PPE in mass estimates of 26%), but Femur or Humerus circumference alone are pretty good too, (PPE of 33 and 27% respectively), whilst length, whilst still highly correlated (r2 =0.95) comes out relatively poorly for mass predictions (Femur and Humerus PPEs of 70% and 50% respectively). Although Sauropods are out at the very edge of the allometric space,the regressions (which include and assess published best estimates for various extinct mega-tetrapods) are pretty compelling. You’re absolutely right though – extrapolating to 70 vs 77 tons is meaningless.

Could it be that the remains in the bonebed are the first reasonably complete remnants of Argentinosaurus huinculensis? The provenance as well as the rock horizon that hosts the bonebed are more-or-less the same as the estimated temporal range of the rock horizon that had yielded the Argentinosaurus huinculensis holotype.

Matt, CoherentSheath – thanks, that’s what I guessed, that there was no Argentinosaurus femur known. CoherentSheath – I suppose that the issue the is that we don’t know then if Argentinosaurus had geometrically similar limbs to those we’ve inferred for the new beastie! I’m still not sure which taxon Pol and colleagues have used to infer their 70000kg previous heaviest beast. It wasn’t Brachiosaurus, the heaviest (even though partly estimated) from Benson et al 2014. It looks like Argentinosaurus may have been heavier, so they have presumably gone for one where the femur and humerus are both known and can be measured, but then why wasn’t that in the Benson et al dataset?

I’m still also not sure why Benson et al had to estimate the Brachiosaurus althithorax humerus circumference. The FMNH P 25107 specimen seems to be the holotype with both femur and humerus known. I wonder why you can measure humerus length but not circumference for it, and the circumference has to be estimated? Perhaps it is partly encased in a jacket or otherwise inaccessible – Diego Pol was seen drilling out the rock around the largest humerus and partly removing the field jacket in order to measure the circumference in situ. I guess circumference measures are a little more complicated than lengths for these big guys! Do we know of a femur and humerus for Brachiosaurus that are a) larger then the holotype, b) associated i.e. likely of the same individual (Benson et al have a notation if the two bones measured were from a bonebed not single individual) and c) that is easily accessible for measurement?

Going through the Benson et al data properly, the length of 2250mm for the MCF PVPH-1 Argentinosaurus femur specimen – is that the somewhat incomplete one that everyone reconstructs as 2.4m+ long? It’s also not the longest measured femur in the dataset – that’s Antarctosaurus wichmannianus at 2280mm, though the circumference F is 796mm, making it more slender than Brachiosaurus (F=940mm, femur length=2030mm). Mike notes that ‘Brachiosaurus has the most gracile humeri of all sauropods’, but I guess this doesn’t apply to the femur.

As far as I can see in the Benson et al data, Turiasaurus is the heaviest sauropod for which both F and H were measured and not one or both estimated. It’s only 4th on the femur circumference F list (848mm), but has a fairly equal humerus circumference value H (755mm) which is the highest measured, so Turiasaurus was a) an all-round chunky kinda sauropod and b) known from both femur and humerus and so could be measured and mass estimated.

Matt, CoherentSheath — thanks, that’s what I guessed, that there was no Argentinosaurus femur known.

You mean no Argentinosaurus humerus, right? There is an (incomplete) femur, but no humeral material at all that I know of.

I’m still also not sure why Benson et al had to estimate the Brachiosaurus althithorax humerus circumference. The FMNH P 25107 specimen seems to be the holotype with both femur and humerus known. I wonder why you can measure humerus length but not circumference for it, and the circumference has to be estimated? Perhaps it is partly encased in a jacket or otherwise inaccessible.

Yes, the humerus is half-encased in a jacket, face down (we should post photos some time), which would make the circumference impossible to measure directly. But the mounted Brachiosaurus skeleton right outside the Field Museum (and the identical one at O’Hare Airport) have casts of that humerus, so measuring the circumference shouldn’t require any equipment more exotic than a stepladder. Maybe the anterior aspect was sculpted — but I doubt it, as there certainly was a time when the humerus was out of its jacket and mounted vertically.

(I don’t know the detailed provenance of all the elements of the Field Museum’s Brachiosaurus mount: to the best of my knowledge, there is no publication describing it, as Janensch (1950b) does for the Berlin Giraffatitan mount. Someone should write one, but I don’t know who even has the information.)

Do we know of a femur and humerus for Brachiosaurus that are a) larger then the holotype, b) associated i.e. likely of the same individual […]

Let me stop you there: the answer is no. There’s no unambiguously referred additional femoral material of Brachiosaurus at all — the only published thing I know of is the Recapture Creek proximal portion mentioned by Jensen (1987), but as he right notes (pp. 604-606) there’s enough of that to make the referral secure, and its brachiosaur identity is only tenative. The only additional humerus I know of is the Potter Creek specimen, described in the same paper and on display in the public gallery of the Smithsonian as USNM 21903. At 213 cm, it’s slightly longer than the humerus of the holotype, but probably a little shorter than that was before the distal end eroded. (Also, I am not 100% certain about the referral, due to the excessive restoration.)

Mike notes that `Brachiosaurus has the most gracile humeri of all sauropods’, but I guess this doesn’t apply to the femur.

My bad, that was a typo (now corrected): my point was that brachiosaurs as a group (not just Brachiosaurus) have gracile humeri. And, no, it doesn’t seem to apply to the femora.

Which is very strange. Why would an animal that carried to much of its mass on its forlimbs have them so much more gracile than the hindlimbs? I have no idea (and don’t know that anyone has ever even proposed a reason). Anyone?

[…] so Turiasaurus was a) an all-round chunky kinda sauropod and b) known from both femur and humerus and so could be measured and mass estimated.

Yes — though only to the extent that you trust estimates based on limb-bone allometry at all, which I am not inclined to do as they beg some of the questions you want to ask. You have to start from the assumption that all animals are equally athletic.

Could it be that the remains in the bonebed are the first reasonably complete remnants of Argentinosaurus huinculensis?

It’s possible. Right now we don’t have any reason to prefer that hypothesis over the idea that it is something new–we simply don’t have any evidence one way or the other. There are single localities in the Morrison Formation with 4-5 genera of sauropods represented (e.g., Apatosaurus, Barosaurus, Camarasaurus, and Diplodocus at both Como Bluff and Dinosaur National Monument), so there is certainly no general ecological barrier to having multiple large sauropods coexisting in the same locality, let alone the same horizon (although there might have been local ecological restrictions acting in some times and places).

And more importantly, if the remnants are indeed from Argentinosaurus, could it tell us about the animal’s range of individual (and possibly sexual) variations?

Doubtful on individual, and almost certainly nothing about sexual variation. So far the number I’ve heard is 150 bones–that’s about 3/4 of the skeleton of ONE individual. And we know already that there are individuals of different sizes in the quarry. We’ll be lucky if there is enough overlapping material to cross-scale and produce a reasonable skeletal reconstruction of the whole animal. Dividing those 150 bones into 5 or 6 piles and then trying to divine anything about individual differences would be challenging at best.

Two points: first, we have a policy of not IDing commercially-held specimens, because we don’t want to even accidentally lend any legitimacy to specimens in private hands.

That said, it looks to me like either both of those photos of the Waugh Quarry femur are suffering a LOT of top-to-bottom compressive distortion, or that femur is too fat to be Brachiosaurus altithorax.

Matt Bonnan and I tried to cover all of the known specimens of Brachiosaurus in our 2004 paper, but it wouldn’t surprise me if there were some unpublished ones we didn’t know about, or if more have come to light in the past decade.

The first one is definitely not Brachiosaurus — it’s far, far too gracile, and too splayed at the foot. Compare it with the photo in today’s post. I’d be interested to know what the heck it was, though, that had a 2.1 m femur this slender. Since it was misinterpreted as Brachiosaurus I guess it was found in the Morrison, which cuts down the options a bit. When you think slender sauropod femur from the Morrison, you think Amphicoelias, so that would be my provisional guess.

The Waugh Quarry specimen is less unlike Brachiosaurus but lacks the fourth trochanter visible in anteroir/posterior view and has more asymmetric distal condyles, so my guess would be that’s not Brachiosaurus either. (Also, it’s tiny — only 1.7 m.)

Finally, the third photo also lacks the prominent trochanter, but otherwise doesn’t look too far wrong. Again, it’s smaller than the holotype.

There are probably 30 specimens out there of which someone at some time has said “eh, I don’t know, maybe Brachiosaurus?” I think the number of solidly referred specimens is very very much less than that. One hears rumours of nice, fairly complete specimens disappearing into private collections, but they’re gone.

Good catch. There’s another thing about that skinny femur that suggests it’s not Brachiosaurus–the distal condyles are beveled so that if they were level, the femur would lean out, not in. That’s a diplodocid thing, not a titanosauriform thing. So MIke’s tentative ID of Amphicoelias is looking good.

Finally, the third photo also lacks the prominent trochanter, but otherwise doesn’t look too far wrong.

The second and third photo are both of the Waugh Quarry femur. Look at the erosion around the proximal end and the big dent toward the distal end. It’s the same bone.

At least on that one, the distal condyles are beveled in the right direction for it to be a titanosauriform. But I still think it’s too fat to be Brachiosaurus.

It will be interesting, when we have more and better material of Morrison brachiosaurs, to see if they really all belong to the same critter. It’s possible that Brachiosaurus is the Pleurocoelus of Morrison titanosauriforms.

Good spot on the second and third of Nima’s femora being the same. Or rather, it was particularly stupid of me not to have spotted it, especially given that super-distinctive pit on the distal end of the anterior face.

It’s not obvious to me that that femur isn’t one of the many basal macronarians currently lumped into Camarasaurus.

[…] Dinosaurs were large (well, many of them were large though not all). There is a new print of a tellurian laying subsequent to a femur hoary of a titanosaur and a bone only looks ginormous. Of march it’s big, but apparently this is about how large these things get. […]

[…] measurements to estimate the masses of the same individuals as 56000 and 34000 kg. When Ian Corfe mentioned this in a comment, my immediate reaction was to be sceptical: “I’m amazed that the two more recent papers […]

A final note – quite a few of the direct quotes from the team seem to be discussing the largest dinosaur or the heaviest dinosaur, not the tallest dinosaur or the dinosaur with the longest limb bones, so I’m fairly certain that’s why they aren’t discussing the limb bone lengths.

Or the other way around. Linear measurements are always easier to grasp; if they had the longest dinosaur, they’d say so.